Heater particularly for a motor vehicle hvac system

ABSTRACT

A motor vehicle HVAC unit includes a housing, preferably a fan, preferably a coolant evaporator for cooling air to be supplied to the vehicle interior, at least two electric resistance heaters for heating the air to be supplied to the vehicle interior and at least one delay circuit, preferably two delay circuits. The at least two electric resistance heaters are suppliable with electric current, and a device is provided for supplying current to at least one of the at least two electric resistance heaters with a time delay relative to another electric resistance heater, and during the turning on or supplying current to the electric resistance heaters a small maximum current peak requirement is to occur at low technical expenditures.

This nonprovisional application claims priority under 35 U.S.C. §119(a)to European Patent Application No. EP09290807.8, which was filed on Oct.21, 2009, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a heater particularly for a motor vehicle HVACsystem according to the preamble of claim 1 and to a method foroperating a heater of this type according to the preamble of claim 12.

2. Description of the Background Art

Motor vehicle HVAC systems are used for heating and cooling air that issupplied to the interior of a motor vehicle. In this regard, electricheaters or resistance heaters are used for heating the air, particularlyin hybrid or electric vehicles. An electric current is passed throughthe electric resistance heaters and because of the electric resistanceof the electric resistance heaters, they become heated, so that the airsupplied to the vehicle interior can be heated by passing the air pastthe electric resistance heaters.

To control different heat outputs of the electric resistance heaters,the electric resistance heaters are supplied with current in pulse widthmodulation (PWM). When the electric resistance heaters are supplied withpulse-width-modulated current, the electric heat output of the electricresistance heaters is controlled to the effect that the pulse widthmodulation is changed. This means that for an increase in the electricheat output the turn-on time is lengthened and the turn-off timeshortened and conversely during a reduction of the electric heat outputthe turn-on time is shortened and the turn-off time increased. Theelectric current for the electric resistance heaters originates from anon-board electrical system as the current source of the motor vehicle.In order not to have a very large maximum current peak requirement forall electric resistance heaters during turning on or supplying currentto the electric resistance heaters, i.e., at the beginning of theturn-on time of the pulse-width-modulated current, thepulse-width-modulated current before being supplied to the individualelectric resistance heaters is delayed in time by a microcontroller. Theelectric resistance heaters thereby have turn-on times that are notsimultaneous but delayed in time and thereby sequential in time. Themaximum current peak requirement for the electric resistance heaters canbe reduced thereby, because all electric resistance heaters are notturned on or supplied with current at the same time; i.e., the turn-ontimes of the electric resistance heaters are not identical.

The microcontroller, which generally has a processor and thereby can runa program or software, is thereby generally arranged in the motorvehicle HVAC system, particularly in the area of the electric resistanceheaters. Microcontrollers of this type are time-consuming to produce,however, and thereby expensive and thereby in addition prone to failureduring operation.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a heaterparticularly for motor vehicle HVAC units and a method for operating aheater of this type, in which heater and method during the turning on orsupplying of electric resistance heaters with current, a small maximumpeak current requirement occurs at low technical cost. The heater shouldbe inexpensive to produce and reliable to operate.

This object is achieved with a heater, particularly for an HVAC unit,comprising a housing, preferably a fan, preferably a coolant evaporatorfor cooling air to be supplied to the vehicle interior, at least twoelectric resistance heaters for heating the air to be supplied to thevehicle interior, whereby the at least two electric resistance heaterscan be supplied with electric current, and a device for supplyingcurrent to at least one electric resistance heater with a time delayrelative to another electric resistance heater, whereby the devicecomprises at least one delay circuit, preferably two delay circuits,and/or the device comprises at least one delay circuit, preferably twodelay circuits.

In particular, the at least one delay circuit is at least one,particularly exclusively, analog delay circuit and/or the at least onedelay circuit has no processor and/or no program can be run by the atleast one delay circuit and/or the at least one delay circuit is anelectric and/or electronic circuit, particularly without a processor.Therefore no digital signals or information can be processed in the atleast one delay circuit. The delay circuit is therefore an electricand/or electronic circuit with a very simple structure, which inparticular has no processor. Therefore, the delay circuit can beproduced simply and at reasonable cost, so that the high cost for anexpensive and time-consuming microcontroller can be economized.

In another embodiment, the at least one delay circuit comprises at leastone capacitor and/or at least one resistor. It is also possible toprovide an inductor in addition.

In a supplementary embodiment, the at least one delay circuit comprisesexclusively at least one capacitor and/or at least one resistor as anelectric and/or electronic component. Because simple electroniccomponents are used, for example, a capacitor and a resistor, the delaycircuit can be produced simply and at reasonable cost.

Preferably, the at least one electric resistance heater can be suppliedwith electric current in pulse width modulation. The supplying of the atleast two electric resistance heaters with current therefore correspondsto the passing of current through the at least two electric resistanceheaters during the turn-on times of the pulse-width-modulated current.

In a variant, at least one electric resistance heater can be suppliedwith pulse-width-modulated current delayed in time relative to anotherelectric resistance heater with the at least one delay circuit. Themaximum current peak requirement for the at least two electricresistance heaters, particularly for all electric resistance heaters,can be reduced thereby at the beginning of the turn-on times.

Expediently, the at least one electric resistance heater is at least onePTC heater. It is especially advantageous, in this case, if the at leastone resistance heater or a majority of electric resistance heaters arecombined into a module and advantageously the electric control unit canbe or is connected to this module. An electric resistance heater isthen, so to speak, a heating section of the module.

In another embodiment, the at least two electric resistance heaters areconnected electrically parallel.

In another embodiment, each of the parallel connected electricresistance heaters are each connected to a parallel power line and theparallel power lines are connected to a central power line.

In a further embodiment, in parallel connected electric resistanceheaters one delay circuit each is connected in series to the parallelconnected electric resistance heaters.

In a supplementary variant, at least two delay circuit devices areconnected parallel and/or in series.

The method of the invention for operating a heater, particularly for avehicle HVAC system, particularly comprises the steps: conduction ofelectric current through at least two electric resistance heaters,preferably conduction of air through the heater of the vehicle HVACsystem, generation of thermal energy by the at least two electricresistance heaters by converting electrical energy into thermal energy,preferably the transfer of the thermal energy generated by the at leasttwo electric resistance heaters to the air to be heated, whichpreferably is passed through the vehicle HVAC system, so that the airbecomes heated, whereby during the supplying of current to the at leasttwo electric resistance heaters, at least one electric resistance heateris supplied with current delayed in time relative to another electricresistance heater, in order to reduce the maximum current peakrequirement for the at least two electric resistance heaters during thesupplying of current and/or the turning on of the at least two electricresistance heaters, whereby the current is delayed in an analog mannerand/or the current is delayed without a program or software being run.

In another embodiment, the current is delayed exclusively in an analogmanner, particularly by at least one delay circuit.

In particular, the current passed through the at least two electricresistance heaters is pulse-width-modulated and preferably the pulsewidth modulation is changed, particularly the turn-on and turn-off timesare changed, in order to control and/or to regulate the electric powerof the at least two electric resistance heaters.

In another embodiment, the current is delayed by at least one delaycircuit in each case for one electric resistance heater.

In another embodiment, the at least two electric resistance heaters aresupplied with current in the high voltage range, for example, with avoltage of at least 60 V, 200 V, or 300 V.

Expediently, the vehicle HVAC system comprises at least one air guidingdevice, particularly a ventilation flap, and/or at least one air passageand/or at least one heat exchanger through which coolant from acombustion engine flows, for heating the air supplied to the vehicleinterior, and/or a control unit.

In a supplementary variant, cooling fins are arranged at the at leasttwo electric resistance heaters, in order to increase the surface forheating the air by current passed through the two electric resistanceheaters.

PTC heaters (PTC: Positive Temperature Coefficient) are current-conducting materials that have an electric resistance and can conductcurrent better at lower temperatures than at higher temperatures. Theirelectric resistance therefore increases with increasing temperature. ThePTC heater generally comprises ceramic, which is a PTC thermistor.Independent of the boundary conditions, such as, e.g., applied voltage,nominal resistance, or volume of air at the PTC heater, a very uniformsurface temperature arises at the PTC heater.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIG. 1 shows a circuit arrangement with three electric resistanceheaters and two delay circuits in a first exemplary embodiment;

FIG. 2 shows a circuit arrangement with three electric resistanceheaters and two delay circuits in a second exemplary embodiment; and

FIG. 3 shows the time voltage course of a pulse-width-modulated currentfor the three electric resistance heaters.

DETAILED DESCRIPTION

A circuit arrangement with three resistance heaters 1, formed as PTCheaters 2, is shown in FIG. 1, particularly for a vehicle HVAC unit (notshown) for heating the air passed through the vehicle HVAC unit.

PTC heaters 2 are connected parallel in this case and are supplied withelectric current by a current source 4, namely, an on-board electricalsystem 5 of the motor vehicle outside the vehicle HVAC system. Currentsource 4 in this case provides current in pulse width modulation. Inthis regard, the current in pulse width modulation is passed fromcurrent source 4 through central power lines 8, as power lines 6, toparallel power lines 7. The electric current in pulse width modulationis passed through PTC heaters 2 by parallel power lines 7. A delaycircuit 3 in each case is built into two of the three parallel powerlines 7. Delay circuit 3 has no processor, i.e., therefore also cannotrun any program or software, and is substantially equipped with simpleelectric and/or electronic components, for example, at least onecapacitor and/or at least one resistor. Delay circuit 3 is thereforeespecially simple and inexpensive to produce.

The time voltage course of the current passed through the three PTCheaters 2 in pulse width modulation is shown in FIG. 3. Here, the time tis plotted on the abscissa, i.e., the horizontal axis. The electriccurrent is passed through PTC heaters 2 in pulse modulation; i.e.,during a turn-on time T_(e), current is passed through PTC heaters 2 andduring a turn-off time T_(a) no current is passed through PTC heaters 2.The duration of the turn-on time T_(e) and the turn-off time T_(a) inthis regard can be changed by current source 4 and thereby the electricheat output of PTC heaters 2 is changed. The longer the turn-on timesT_(e) and the shorter the turn-off times T_(a), the higher the electricheat output provided by PTC heaters 2 and conversely. Therefore, duringthe supplying of current or turning on of PTC heaters 2—i.e., at thebeginning of the turn-on time point T_(e), the start of the supplying ofcurrent or the start of the turn-on times T_(e) does not occursimultaneously in all PTC heaters 2—the current provided by currentsource 4 in pulse width modulation is delayed in time by delay circuits3. The time voltage course of the pulse-width-modulated current for thePTC heater 2, shown at the top in FIG. 1, is shown in the bottom curvein FIG. 3. The middle curve in FIG. 3 shows the time voltage course ofthe pulse-width-modulated current for the middle PTC heater in FIG. 1and the top curve in FIG. 3 shows the time voltage curve of thepulse-width-modulated current of PTC heaters 2 shown at the bottom inFIG. 1. The start of the turn-on time T_(e) here is delayed in each caseby a delay time Δt. Delay circuit 3 for the middle PTC heater, shown inFIG. 1, thereby delays the current provided by current source 4 by thedelay time Δt and the delay circuit 3, for the bottom PTC heater 2 inFIG. 1, therefore delays the current from current source 4 by two delaytimes Δt. A phase offset of the pulse-width-modulated current thereforeoccurs in PTC heaters 2 and parallel power lines 7. The maximum currentpeak requirement for the three PTC heaters 2 at the beginning of theturn-on times T_(e) can be reduced thereby.

The circuit arrangement with three PTC heaters 2 and two delay circuits3 is shown in a second exemplary embodiment in FIG. 2. Substantiallyonly the differences with respect to the first exemplary embodimentaccording to FIG. 1 will be described below. Delay circuit 3 for PTCheater 2, shown at the bottom in FIG. 2, is not connected directly tocentral power line 8, but is connected to parallel power line 7 betweendelay circuit 3 and middle PTC heater 2. Delay circuit 3 thereforereceives the already delayed current, which has been delayed by delaycircuit 3 for the middle PTC heater 2. The delay times Δt of delaycircuits 3 for the middle PTC heater 2 and for the bottom PTC heater 2are thereby the same. Because of the supplying of delay circuit 3 forthe bottom PTC heater 2 with the already delayed current from delaycircuit 3 of the middle PTC heater 2, also in the second exemplaryembodiment the time voltage course of the pulse-width-modulated current,shown in FIG. 3, occurs again in the three electric resistance heaters1, although both delay circuits 3 have the same delay times Δt.

Overall, substantial advantages are associated with the vehicle HVACsystem of the invention and the method of the invention for operating avehicle HVAC system. Instead of using a time-consuming and costlymicrocontroller as a device for supplying the electric resistanceheaters 1 with electric current in a delayed manner, as occurs in thestate of the art, a simple and inexpensive delay circuit 3 with ananalog structure is used, so that considerable manufacturing costs canbe saved as a result.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are to beincluded within the scope of the following claims.

1. A heater comprising: at least two electric resistance heaters forheating the air to be supplied to the vehicle interior, whereby the atleast two electric resistance heaters can be supplied with electriccurrent, and a device for supplying current to at least one electricresistance heater with a time delay relative to another electricresistance heater, wherein the device comprises at least one delaycircuit, preferably two delay circuits.
 2. The heater according to claim1, wherein the at least one delay circuit is at least one, particularlyexclusively, analog delay circuit and/or the at least one delay circuithas no processor and/or no program can be run by the at least one delaycircuit and/or the at least one delay circuit is an electrical and/orelectronic circuit, particularly without a processor.
 3. The heateraccording to claim 1, wherein the at least one delay circuit comprisesat least one capacitor and/or at least one resistor.
 4. The heateraccording to claim 3, wherein the at least one delay circuit comprisesexclusively at least one capacitor and/or at least one resistor aselectric and/or electronic components.
 5. The heater according to claim1, wherein the at least two electric resistance heaters can be suppliedwith electric current in pulse width modulation.
 6. The heater accordingto claim 5, wherein a first one of the at least two electric resistanceheaters can be supplied with pulse-width-modulated current delayed intime relative to another one of the at least two electric resistanceheaters with the at least one delay circuit.
 7. The heater according toclaim 1, wherein at least one of the at least two electric resistanceheaters is at least one PTC heater.
 8. The heater according to claim 1,wherein the at least two electric resistance heaters are connectedelectrically parallel.
 9. The heater according to claim 8, wherein eachof the parallel connected electric resistance heaters are each connectedto a parallel power line and the parallel power lines are connected to acentral power line.
 10. The heater according to claim 8, wherein inparallel connected electric resistance heaters one delay circuit each isconnected in series to the parallel connected electric resistanceheaters.
 11. The heater according to claim 10, characterized in that atleast two delay circuit devices are connected parallel and/or in series.12. A method for operating a heater, particularly for a vehicle HVACsystem according to claim 1, comprising the steps: conduction ofelectric current through at least two electric resistance heaters,preferably conduction of air through the heater, generation of thermalenergy by the at least two electric resistance heaters by convertingelectrical energy into thermal energy, preferably the transfer of thethermal energy generated by the at least two electric resistance heatersto the air to be heated, so that the air becomes heated, whereby duringthe supplying of current to the at least two electric resistanceheaters, at least one electric resistance heater is supplied withcurrent delayed in time relative to another electric resistance heater,in order to reduce the maximum current peak requirement for the at leasttwo electric resistance heaters during the supplying of current and/orturning on of the at least two electric resistance heaters, wherein thecurrent is delayed in an analog manner and/or the current is delayedwithout a program or software being run.
 13. The method according toclaim 12, wherein the current is delayed exclusively in an analogmanner, particularly by at least one delay circuit.
 14. The methodaccording to claim 12, wherein the current passed through the at leasttwo electric resistance heaters is pulse-width-modulated and preferablythe pulse width modulation is changed, particularly the turn-on andturn-off times are changed, in order to control and/or to regulate theelectric power of the at least two electric resistance heaters.
 15. Themethod according to claim 12, wherein the current is delayed by at leastone delay circuit in each case for one electric resistance heater.